Methods for the remote activation of a function present in a motor vehicle are known. These methods are known under the name of a “hands-free” method for accessing the vehicle and/or starting the vehicle. In such methods, the person authorized to perform the activation, often the driver of the vehicle, possesses an electronic key or an electronic fob as activation means for performing unlocking or locking of the opening elements and/or making it possible to start the vehicle corresponding thereto with an activation module in the manner described above.
It is possible for the authorized person to carry the electronic key or fob on himself or leave it in a bag that he carries to perform these actions. Such systems for implementing such what are known as “hands-free” unlocking methods are called for example passive access and start engine systems, and grouped together under the term PASE. These “hands-free” systems are particularly advantageous because the authorized person does not need to hold his key or his fob in his hand while pointing it for example at the vehicle.
For a passive access and engine start system, a method of attack, called a relay attack, has been developed by criminals who are not authorized to activate a function present in the vehicle. Such a method of attack makes it possible, for example in order to perform starting, to convince the activation module that the activation means is located inside the vehicle, whereas the apparatus simulating the activation means and the criminal manipulating it are outside the vehicle.
The solutions that are currently implemented against a relay attack do not make it possible to guarantee 100% protection against malicious activation. It has therefore been proposed to temporarily suspend the activation of the requested function after a certain number of unsuccessful activation attempts. This makes it possible to discourage criminals from attacking the system by not allowing them to continue the relay attack.
By contrast, such a solution of suspending the activation has the disadvantage of locking the activation for activation attempts that are unsuccessful even though they do not have any malicious nature as they are performed by an authorized person. This is the case when the activation means is not recognized by the activation module as it is outside of a detection zone or when the transmission between activation means and activation module is subject to interference from electronic apparatuses external to the activation system, for example but not exclusively from mobile telephones situated close to the vehicle.
In the case of use of the activation means that is authorized but leads to an unsuccessful activation attempt, the authorized person, not understanding why his activation means is not working, will tend to repeat his start requests while still holding his activation means in his hand. It is possible that this takes the activation means out of a zone of non-detection, but it may also be the case that this does not change anything with regard to the lack of detection and that the authorized person then himself locks the activation by performing too many unsuccessful activation attempts and exceeding a maximum number of unsuccessful activation attempts that is predetermined for the security of the activation method.